Utilisation of waste bread for fermentative succinic acid production

A novel biorefinery concept of utilising waste bread as a sole nutrient source for the production of a nutrient rich feedstock for the fermentative succinic acid production by Actinobacillus succinogenes has been developed. Waste bread was used in the solid-state fermentations of Aspergillus awamori and Aspergillus oryzae that produce enzyme complexes rich in amylolytic and proteolytic enzymes, respectively. The resulting fermentation solids were added directly to a bread suspension to generate a hydrolysate containing over 100 g/L glucose and 490 mg/L free amino nitrogen (FAN). A first-order kinetic model was used to describe the effect of initial bread mass ratio on glucose and FAN profiles. The bread hydrolysate was used as the sole feedstock for A. succinogenes fermentations, which led to the production of 47.3 g/L succinic acid with a yield and productivity of 1.16 g SA/g glucose and 1.12 g/L h. This corresponds to an overall yield of 0.55 g succinic acid per g bread. This is the highest succinic acid yield compared from other food waste-derived media reported to date. The proposed process could be potentially utilised to transform no-value food waste into succinic acid, one of the future platform chemicals of a sustainable chemical industry.

► This paper presents a novel process to convert waste bread to succinic acid.
► Enzymatic hydrolysis yielded 0.47 g glucose/g bread at 100% starch conversion.
► Enzymatic hydrolysis yielded 2.55 mg FAN/g waste bread.
► Bacterial fermentation on the hydrolysate yielded 1.16 g succinic acid/g glucose.
► This is the highest substrate to succinic acid yield among other food-derived media.